Process for the preparation of unsaturated acids from unsaturated aldehydes

ABSTRACT

Methacrylic acid or acrylic acid are produced by the oxidation of methacrolein or acrolein, respectively, with molecular oxygen in the vapor phase in the presence of a catalytic oxide of molybdenum, phosphorus, arsenic, at least one element selected from the group consisting of U, Ti, Nb, Re, Pb, Zn, and Ga, oxygen, and optionally, at least one of Cu, a rare earth element, Ag, Ta, In, Th, Cd, Tl, alkaline earth metal, NH 4 , Cl, Ni, Al and Ge.

REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 733,735 filed Oct. 19,1976, now U.S. Pat. No. 4,085,065.

BACKGROUND OF THE INVENTION

A number of catalysts are known to be effective for the oxidation ofacrolein or methacrolein to acrylic acid or methacrylic acid,respectively. However, the yields obtained using the catalysts for thepreparation of methacrylic acid are low. West German Provisional Pat.No. 2,048,620 discloses catalysts containing the oxides of molybdenum,phosphorus, and arsenic for the oxidation of methacrolein and acroleinto methacrylic acid and acrylic acid, respectively. U.S. Pat. No.3,761,516 discloses catalysts containing oxides of molybdenum, arsenicand phosphorus on a support, especially Al₂ O₃, having externalmacropores and a surface not greater than 2 m² /g.

The present invention is a result of a search for more efficient anddesirable catalysts for the production of acrylic acid and methacrylicacid. Unexpectedly higher yields of and selectivities to acrylic acidand methacrylic acid are obtained by the vapor phase oxidation ofacrolein and methacrolein, respectively, with molecular oxygen in thepresence of the new and useful catalysts of the present invention.

SUMMARY OF THE INVENTION

It has been discovered according to the present invention in the processfor the preparation of acrylic acid or methacrylic acid by the oxidationof acrolein or methacrolein, respectively, with molecular oxygen in thevapor phase at a reaction temperature of about 200° C. to about 500° C.in the presence of an oxide catalyst, and optionally in the presence ofsteam, the improvement comprising

USING AS A CATALYST A CATALYST OF THE FORMULA

    X.sub.a Y.sub.b Mo.sub.12 P.sub.c As.sub.d O.sub.x

wherein

X is at least one element selected from the group consisting of U, Ti,Nb, Re, Pb, Zn, and Ga;

Y is Cu, a rare earth element, Ag, Ta, In, Th, Cd, Tl, an alkaline earthmetal, NH₄, Cl, Ni, Al and Ge; and wherein

a is 0.001 to 10;

b is 0 to 10;

c is 0.01 to 5;

d is 0.01 to 5;

x is the number of oxygens required to satisfy the valence states of theother elements present.

The surprisingly advantageous catalysts of this invention give improvedyields of acrylic acid and methacrylic acid from acrolein andmethacrolein, respectively, in an efficient, convenient, and economicalmanner at a relatively low temperature.

The most significant aspect of the present invention is the catalystemployed. The catalyst may be any of the catalysts delineated by theabove formula. The catalysts can be prepared by a number of differenttechniques described in the art, such as coprecipitation of solublesalts and calcination of the resulting product.

The catalysts of the invention have preferred limitations on theircomposition. Preferred are catalysts wherein a is 0.001 to 3, catalystswherein b is 0.001 to 3; and catalysts wherein b is zero.

Especially preferred are catalysts wherein each of the elementsdescribed by X is separately incorporated into the catalyst. This isconveniently accomplished by setting X independently equal to thevarious elements. Catalysts of particular interest are described whereinY is at least one element selected from the group consisting of a rareearth element, Al, Ag and Cu.

In the catalyst preparations, the various elements of the catalyst arecombined, and the final product is calcined to obtain the catalyst. Anumber of methods of combining the elements of the catalyst andcalcining the resultant product are known to those of skill in the art.In the broad concept of the invention, the particular method ofpreparing the catalysts is not critical.

There are, however, methods of preparing the catalysts that have beenfound to be preferred. One preferred preparation involves thepreparation of the catalysts in an aqueous slurry or solution ofmolybdenum, phosphorus and/or arsenic containing components, and addingthe remaining components; evaporation of this aqueous mixture; andcalcination of the resulting catalysts. Suitable molybdenum compoundsthat may be employed in the preparation of the catalysts delineated bythe above formula include molybdenum trioxide, phosphomolybdic acid,molybdic acid, ammonium heptamolybdate and the like. Suitable phosphoruscompounds that may be employed in the preparation of the catalystsinclude ortho-phosphoric acid, metaphosphoric acid, triphosphoric acid,phosphorus halide or oxyhalide and the like. The remaining components ofthe catalysts may be added as oxide, acetate, formate, sulfate, nitrate,carbonate, oxyhalide, or halide and the like.

Excellent results are obtained by refluxing phosphoric acid, an arseniccontaining compound, and molybdenum trioxide, or ammonium heptamolybdatein water for about 1/2 hour to 3 hours, however, commercialphosphomolybdic acid may be effectively utilized; adding the remainingcomponents to the aqueous slurry and boiling to a thick paste; drying at110° C. to 120° C. in air; and calcining the resulting catalysts.

The calcination of the catalyst usually is accomplished by heating thedry catalytic components at a temperature of about 200° C. to about 700°C. The preferred procedure of the invention is wherein the catalyst iscalcined at a temperature of 325° C. to 425° C.

The reactants of the reaction of the invention are methacrolein oracrolein and oxygen. Molecular oxygen is normally supplied to thereaction in the form of air, but oxygen gas could also be employed.About 0.5 to about 4 moles of oxygen are normally added per mole ofmethacrolein.

The reaction temperature may vary as different catalysts are employed.Normally, temperatures of about 200° C. to about 500° C. are employedwith temperatures of 250° C. to 370° C. being preferred.

The catalyst may be used alone or a support could be employed. Suitablesupports include silica, alumina, Alundum, silicon carbide, boronphosphate, zirconia and titania. The catalysts are conveniently used ina fixed-bed reactor using tablets, pellets or the like or in a fluid-bedreactor using a catalyst having a particle size of less than about 300microns. When a fluid-bed reactor is employed, preferred catalysts arein the form of microspheroidal particles. The contact time may be as lowas a fraction of a second or as high as 20 seconds or more. The reactionmay be conducted at atmospheric, superatmospheric or subatmosphericpressure, with absolute pressures of about 0.5 to about 4 atmospheresbeing preferred.

Excellent results are obtained using a coated catalyst consistingessentially of an inert support material having a diameter of at least20 microns and an outer surface and a continuous coating of said activecatalyst on said inert support strongly adhering to the outer surface ofsaid support. The special coated catalyst consists of an inner supportmaterial having an outside surface and a coating of the active catalyticmaterial on this outside surface. These catalysts can be prepared by anumber of different methods.

The support material for the catalyst forms the inner core of thecatalyst. This is an essentially inert support and may havesubstantially any particle size although a diameter of greater than 20microns is preferred. Especially preferred in the present invention foruse in a commercial reactor are those supports which are spherical andwhich have a diameter of about 0.2 cm to about 2 cm. Suitable examplesof essentially inert support materials include: Alundum, silica,alumina, alumina-silica, silicon carbide, titania and zirconia.Especially preferred among these supports are Alundum, silica, aluminaand alumina-silica.

The catalysts may contain essentially any proportions of support andcatalytically active material. The limits of this relationship are onlyset by the relative ability of the catalyst and support material toaccommodate each other. Preferred catalysts contain about 10 to about100 percent by weight of catalytically active material based on theweight of the support.

The preparation of these coated catalysts can be accomplished by varioustechniques. The basic method of preparing these catalysts is bypartially wetting the support material with a liquid and then contactingthe support material with a powder of the catalytically active materialand gently agitating the mixture until the catalyst is formed. Thegentle agitation is most conveniently accomplished by placing thepartially wet support in a rotating drum or jar and adding the powderedactive catalytic material.

Using the catalysts of the invention in the preparation of methacrylicacid or acrylic acid, excellent yields are obtained in a convenientreaction with low amounts of byproducts.

SPECIFIC EMBODIMENTS Comparative Example A to D and Examples 1 to 47

Comparison of catalysts containing promoters of invention with basecatalyst in the preparation of methacrylic acid.

A 20 cc. fixed-bed reactor was constructed of a 1.3 cm stainless steeltubing. Catalysts prepared as described below were charged to thereactor and heated to the reaction temperature under a flow of air and afeed of methacrolein/air/nitrogen/steam of 1/5.7/4.6/8.7 was fed overthe catalyst at an apparent contact time of 2 to 4 seconds. The reactorwas run under the reaction conditions for 1 to 6 hours and the productwas collected and analyzed.

Comparative Example A and Examples 1 to 23

The catalysts were prepared as follows:

Comparative Example A 25% Mo₁₂ P₁ As₀.5 O_(x) + 75% Alundum

A solution was prepared consisting of 211.88 grams of ammoniumheptamolybdate, (NH₄)₆ Mo₇ O₂₄.4H₂ O, (1.2 mole Mo), 500 mls. distilledwater at 60° C. and 7.94 grams of ammonium arsenate, NH₄ H₂ AsO₄, (0.05mole As), as solution in 25 mls. distilled water. A white precipitateformed which was heated to about 100° C. for 2 hours. To this mixturewas added 11.53 grams of 85% solution phosphoric acid (0.10 mole P).One-half hour later 5.0 grams of hydrazine hydrate was added. The slurrywas evaporated to a thick paste, dried overnight in an oven at 110° to120° C., and ground and screened to less than 80 mesh. This powder wascoated on 1/8 inch SA 5223 Alundum balls by taking 50 grams of Alundum,partially wetting the Alundum with 1.8 grams of water and adding 16.7grams of active catalyst prepared above in five equal portions. Duringand after each addition, the Alundum was rolled in a glass jar. Thepowder was evenly coated onto the surface of the Alundum and the finalproduct was dried. A hard uniform material was obtained that consistedof an inner core of the Alundum support with the continuous, stronglyadhering coat of the powder on the outside surface of the support. Thismaterial was then calcined for 1 hour at 370° C. in 40 ml./min. air toform the active catalyst.

EXAMPLE 1 25%U₀.25 Mo₁₂ P₁ As₀.5 O_(x) + 75% Alundum

A solution was prepared consisting of 105.9 grams of ammoniumheptamolybdate, (NH₄)₆ Mo₇ O₂₄.4H₂ O, (0.6 mole Mo), 700 mls. ofdistilled water at 60° C. and 4.0 grams of ammonium arsenate, NH₄ H₂AsO₄, (0.025 mole As) as solution in 25 mls. of water. A whiteprecipitate formed which was heated at 100° C. about 1/2 hour. To thismixture was added 5.3 grams of uranyl acetate (0.0125 mole U), followedby the addition of 5.8 grams of 85% solution phosphoric acid (0.05 moleP). One-half hour later 2.5 grams of hydrazine hydrate were added. Theslurry was evaporated to a thick paste, dried overnight in an oven at110° to 120° C., and ground and screened to less than 80 mesh size. Thecatalyst was then coated to 25% active level on 1/8 inch SA 5223 Alundumballs. Calcination was the same as in Comparative Example A.

EXAMPLE 2 25% Ti₀.2 Mo₁₂ P₁ As₀.5 O_(x) + 75% Alundum

This catalyst was prepared in the same manner described in Example 1,except 7.72 grams of 20% titanium trichloride solution were employed andhydrazine hydrate was deleted in the catalyst preparation.

EXAMPLE 3 25% (Rare earth mixture)₀.2 Ti₀.1 Mo₁₂ P₁ As₀.5 O_(x) + 75%Alundum

This catalyst was prepared in the same manner described in Example 1,except 3.54 grams of rare earth chloride mixture, 0.5 grams of hydrazinehydrate were employed and 3.85 grams of 20% titanium trichloridesolution were added.

EXAMPLES 4 TO 19 Preparation of the Catalysts 25% X_(a) Y_(b) Mo₁₂ P₁As₀.5 O_(x) + 75% Alundum

Various catalysts of the invention were prepared. The catalysts wereprepared according to the procedure of Example 1, using 105.9 grams ofammonium molybdate, 700 mls. of 60° C. distilled water and 4.0 grams ofammonium arsenate in solution of 25 mls. of water. The catalyticcomponents delineated by X and/or Y were added immediately preceding theaddition of 5.8 grams of 85% solution phosphoric acid. 2.5 grams ofhydrazine hydrate were added in all preparations, except no hydrazinewas added in Examples 8, 10, 12 and 18; 1.0 gram of hydrazine was addedin Example 14. To prepare the catalysts, the following compounds andamounts were used:

    ______________________________________                                        Example                                                                             Element      Compound        Amount, g.                                 ______________________________________                                        4     Nb.sub.0.25  niobium chloride                                                                              3.37                                       5     Pb.sub.0.25  lead acetate    4.75                                       6     Zn.sub.0.25  zinc acetate    2.75                                       7     Re.sub.0.25  rhenium sesquioxide                                                                           3.03                                       8     Ag.sub.0.1 Ti.sub.0.2                                                                      20% titanium trichloride                                                                      7.72                                                          solution                                                                      silver acetate  0.8                                        9     Ag.sub.0.1 Zn.sub.0.2                                                                      zinc acetate    2.19                                                          silver acetate  0.8                                        10    Nb.sub.0.05 Ti.sub.0.2                                                                     niobium chloride                                                                              0.67                                                          20% titanium trichloride                                                      solution        7.72                                       11    Re.sub.0.1 Cu.sub.0.25                                                                     rhenium sesquioxide                                                                           1.21                                                          copper acetate  2.48                                       12    Ti.sub.0.15 Zn.sub.0.1                                                                     20% titanium chloride                                                                         5.78                                                          zinc acetate    1.1                                        13    Zn.sub.0.1   zinc acetate    1.09                                                          rare earth                                                       (rare earth  chloride mixture                                                                              3.54                                             mixture).sub.0.2                                                                           (Moly Corp.                                                                   Product No.4700)                                           14    Ti.sub.0.05 Cu.sub.0.05                                                                    20% titanium chloride                                                                         1.92                                             (rare earth  copper acetate  0.50                                             mixture).sub.0.2                                                                           rare earth      3.54                                                          chloride mixture                                           15 Zn.sub.0.05 Cu.sub.0.05                                                          zinc acetate 0.55                                                             (rare earth  copper acetate  0.50                                             mixture).sub.0.2                                                                           rare earth      3.54                                                          chloride mixture                                           16    Ga.sub.0.25  gallium oxide   1.1                                        17    Zn.sub.0.2 Al.sub.0.05 Cu.sub.0.05                                                         zinc acetate    2.19                                                          aluminum chloride                                                                             0.6                                                           copper acetate  0.50                                       18    Ti.sub.0.2 Rare earth.sub.0.05                                                             20% titanium chloride                                                                         7.7                                              Cu.sub.0.05  Moly Corp. rare earth                                                         mixture (4700)  0.90                                                          copper acetate  0.50                                       19    Rare earth.sub.0.1 Pb.sub.0.2                                                              lead acetate    3.8                                                           rare earth mixture                                                                            1.77                                       ______________________________________                                    

EXAMPLE 20 25% Mo₁₂ P₁ As₀.5 Nb₀.25 Ag₀.05 O_(x) + 75% Alundum

This catalyst was prepared in the same manner described in Example 1,except that 34.25 grams of ammonium molybdate, 150 mls. water, 1.28grams of ammonium arsenate, 0.537 grams niobium chloride, 0.134 grams ofsilver acetate, 1.86 grams of 85% phosphoric acid, and 0.8 grams ofhydrazine hydrate were employed.

EXAMPLE 21 25% Mo₁₂ P₁ As₀.5 Nb₀.25 Cu₀.1 O_(x) + 75% Alundum

This catalyst was prepared in the same manner as described in Example 4,except 0.322 grams of copper acetate were added in addition to theniobium chloride.

EXAMPLE 22 25% Zn₀.2 Al₀.08 Cu₀.05 Mo₁₂ P₁.32 As₀.5 O_(x) + 75% Alundum

This catalyst was prepared in the same manner described in Example 17,except that 0.96 grams of aluminum chloride hydrate and 7.6 grams of 85%phosphoric acid were employed.

EXAMPLE 23 25% Re₀.1 Al₀.091 Cu₀.05 Mo₁₂ P₁.32 As₀.5 O_(x) + 75% Alundum

This catalyst was prepared in the same manner described in Example 22,except that 1.1 grams of aluminum chloride hydrate and 1.21 grams of Re₂O₇ were employed.

Comparative Examples B to D and Examples 24 to 47

The results of the experiments in the oxidation of methacrolein toproduce methacrylic acid are shown in the TABLE below. The followingdefinitions are used in measuring the carbon atoms in the feed and theproducts. ##EQU1## In the same manner described above, catalysts of theinvention may be effectively utilized in the preparation of acrylic acidfrom acrolein.

                                      TABLE                                       __________________________________________________________________________    Performance of Catalysts Containing Promoters of Invention Compared With      Base Catalyst in the Preparation of Methacrylic Acid                                                          Results, %                                                              Reaction                                                                            Methacrylic                                   Example                                                                             Catalyst            Temp. ° C                                                                    Acid     Acetic Acid                                                                          Total Conversion                                                                       Selectivity          __________________________________________________________________________    Comp.                                                                             B 25%Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x + 75% Alundum                                             326   19.6     0.5    26.0     75.0                     C 25%Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x + 75% Alundum                                             350   43.0     1.9    56.0     76.0                     D 25%Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x + 75% Alundum                                             376   57.0     4.8    83.0     68.0                     24                                                                              25%U.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x + 75%                                          329ndum                                                                             61.0     4.8    83.0     73.6                     25                                                                              25%Ti.sub.0.2 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x + 75%                                          315ndum                                                                             66.5     5.1    84.0     79.0                     26                                                                              25%R.E..sub.0.2 Ti.sub.0.1 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                   356   55.2     7.2    85.5     64.9                       75% Alundum                                                                 27                                                                              25%Nb.sub.0.25 Mo.sub.12 P.sub.1 As.sub. 0.5 O.sub.x                                              350   50       2.2    59.0     84.0                       75% Alundum                                                                 28                                                                              25%Nb.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                               376   60.0     2.4    73.0     81.0                       75% Alundum                                                                 29                                                                              25%Pb.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                               343   65.7     2.8    79.0     83.0                       75% Alundum                                                                 30                                                                              25%Zn.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                               343   65.3     6.2    90.0     72.0                       75% Alundum                                                                 31                                                                              25%Re.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                               358   63.1     3.7    80.0     78.0                       75% Alundum                                                                 32                                                                              25%Ag.sub.0.1 Ti.sub.0.2 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                     334   54.8     6.0    77.7     70.6                       75% Alundum                                                                 33                                                                              25%Ag.sub.0.1 Zn.sub.0.2 Mo.sub.12 P.sub.1 As.sub.0.05 O.sub.x                                    346   61.3     4.4    79.8     76.7                       75% Alundum                                                                 34                                                                              25%Ag.sub.0.05 Nb.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                   374   59.3     5.2    83.1     71.4                       75% Alundum                                                                 35                                                                              25%Ti.sub.0.2 Nb.sub.0.05 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                    344   60.8     6.2    84.8     71.7                       75% Alundum                                                                 36                                                                              25%Re.sub.0.1 Cu.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                    342   73.4     3.4    88.8     82.6                       75% Alundum                                                                 37                                                                              25%Ti.sub.0.15 Zn.sub.0.1 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                    347   65.5     4.9    85.1     77.0                       75% Alundum                                                                 38                                                                              25%R.E..sub.0.2 Zn.sub.0.1 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                   321   61.3     4.0    76.3     80.3                       75% Alundum                                                                 39                                                                              25%R.E..sub.0.2 Ti.sub.0.05 Cu.sub.0.05 Mo.sub.12 P.sub.1                                         332   62.0     5.0    84.8     73.1                       As.sub.0.5 O.sub.x + 75% Alundum                                            40                                                                              25%R.E..sub.0.2 Zn.sub.0.05 Cu.sub.0.05 Mo.sub.12 P.sub.1                                         330   67.2     4.6    84.5     79.5                       As.sub.0.5 O.sub.x + 75% Alundum                                            41                                                                              25%Ga.sub.0.25 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x + 75%                                         370ndum                                                                             62.8     4.9    84.5     74.3                     42                                                                              25%Zn.sub.0.2 Al.sub.0.05 Cu.sub.0.05 Mo.sub.12 P.sub.1 As.sub.0.5            O.sub.x             327   75.3     4.1    91.8     82                         + 75% Alundum                                                               43                                                                              25%Ti.sub. 0.2 Rare earth.sub.0.05 Cu.sub.0.05                                                    328   66.9     5.1    89.1     75.1                       Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x + 75% Alundum                          44                                                                              25%Nb.sub.0.25 Cu.sub.0.1 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                    346   66.3     7.5    89.8     73.9                       + 75% Alundum                                                               45                                                                              25%R.E..sub.0.1 Pb.sub.0.2 Mo.sub.12 P.sub.1 As.sub.0.5 O.sub.x                                   342   59.5     4.8    79.6     74.4                       75% Alundum                                                                 46                                                                              25%Zn.sub.0.2 Al.sub.0.08 Cu.sub.0.05 Mo.sub.12 P.sub.1.32 As.sub.0.          5                   344   76.1     2.6    90.6     83.8                       O.sub.x + 75% Alundum                                                       47                                                                              25%Re.sub.0.1 Al.sub.0.091 Cu.sub.0.05 Mo.sub.12 P.sub.1.32                                       343   69.0     4.1    83.2     82.8                       As.sub.0.5 O.sub.x + 75% Alundum                                        __________________________________________________________________________

We claim:
 1. In the process for the production of acrylic acid andmethacrylic acid by the oxidation of acrolein and methacroleinrespectively, with molecular oxygen in the vapor phase at a reactiontemperature of about 200° C. to about 500° C. in the presence of anoxide catalyst, and optionally in the presence of steam, the improvementcomprising using as the catalyst a catalyst of the formula

    X.sub.a Y.sub.b Mo.sub.12 P.sub.c As.sub.d O.sub.x

wherein X is at least one element selected from the group consisting ofU, Ti, Nb, Re, Zn, and Ga; Y is at least one element selected from thegroup consisting of Cu, a rare earth element, Ag, Ta, In, Th, Cd, Tl,NH₄, Cl, Ni, Al and Ge; and wherein a is 0.001 to 10; b is 0 to 10; c is0.01 to 5; d is 0.01 to 5; x is the number of oxygens required tosatisfy the valence states of the other elements present.
 2. The processof claim 1 wherein a is 0.001 to
 3. 3. The process of claim 1 wherein bis 0.001 to
 3. 4. The process of claim 1 wherein b is zero.
 5. Theprocess of claim 1 wherein X is uranium.
 6. The process of claim 1wherein X is titanium.
 7. The process of claim 1 wherein X is niobium.8. The process of claim 1 wherein X is rhenium.
 9. The process of claim1 wherein X is zinc.
 10. The process of claim 1 wherein X is gallium.11. The process of claim 1 wherein X is titanium and niobium.
 12. Theprocess of claim 1 wherein X is titanium and zinc.
 13. The process ofclaim 1 wherein Y is at least one element selected from the groupconsisting of Cu, a rare earth element, Al, and Ag.
 14. The process ofclaim 1 wherein X is rhenium and Y is copper.
 15. The process of claim 1wherein the active catalytic material is coated on an inert support. 16.The process of claim 15 wherein the catalyst consists essentially of aninert support material having a diameter of at least 20 microns and anouter surface and a continuous coating of said active catalyst stronglyadhering to the outer surface of said support.
 17. The process of claim16 wherein the active catalyst is about 10 to about 100 percent byweight of the inert support.
 18. The process of claim 16 wherein thesupport is selected from the group consisting of silica, alumina,alumina-silica, silicon carbide, titania and zirconia.
 19. The processof claim 16 wherein the particle size of the inert support is 0.2 cm. to2 cm.
 20. The process of claim 1 wherein methacrylic acid is preparedfrom methacrolein.